This invention relates in general to pest control using microwave energy, and in particular to the use of Super High Frequency (SHF) and Extremely High Frequency (EHF) band microwaves that kill insects in granular materials without the use of chemicals.
The principle of using microwaves as a pesticide in grain and granular materials has been known, but it has been determined that effective and consistent mortality rates are only possible when the grain in unpacked, mixed with air, and fairly uniform in density for effective microwave penetration.
The search for an operating frequency which would lead to enhanced selective heating of insects in the Extremely High Frequency (EHF) and Super High Frequency (SHF) ranges is motivated by the need to develop alternatives to certain important agricultural chemical pesticides for the treatment of stored products which are to be banned by the Clean Air Act by the year 2001. Operation at discrete frequencies in the microwave and millimeter wave ranges, including Industrial Scientific and Medical (ISM) frequencies specified in the U.S. Code of Federal Regulations (47 C.F.R., part 2), is attractive because of the availability of recently developed high-power oscillators with high continuous outputs and efficiencies at those frequencies. Unlike the relatively low-power microwave and lower frequency heaters, operating at frequencies less than or equal to 2.45 GHz, the EHF and SBF high-power sources offer the possibility of continuous processing of the treated product at high throughput rates while taking advantage of the electromagnetic shielding inherent in the waveguide-like piping or duct systems that are common in transport systems at grain storage facilities.
There is a need for a consistently effective microwave granular treatment device and microwave range that effects high mortality rates while maintaining temperatures within acceptable limits.